BP CEO Tony Hayward told a congressional committee Thursday that he was "deeply sorry" for the massive oil spill in the Gulf of Mexico.

The April 20 explosion and fire aboard the Deepwater Horizon drilling rig leased by BP and the resulting oil spill "never should have happened," Hayward said sombrely. "And I'm deeply sorry that it did."

He said he was "personally devastated" by the deaths of the 11 men who died when the rig exploded, acknowledging the deaths had a "profound impact" on the men's friends and family members.

"I understand the seriousness of the situation," he continued. "I know that only actions and results, not mere words, ultimately can give you the confidence you seek.

"I give my pledge as the leader of BP that we will not rest until we make this right."

Hayward was much more forthcoming with his apology than with answers to lawmakers' questions about what might have caused the explosion.

"I think it's too early to reach conclusions," Hayward said when confronted with abundant evidence that BP had cut corners and ignored safety to save money. "I had no prior knowledge or involvement in the drilling of this well, none whatsoever."

Democratic Representative Henry Waxman, the chairman of the House committee on energy and commerce, warned Hayward not to withhold information from investigators looking into the causes of the explosion.

"They're going to have a hard time reaching conclusion if you stonewall them, which is what we seem to be getting today," Waxman said.

"I'm not stonewalling," Hayward said. "I was simply not involved in the decision-making process."

A protester, Diane Wilson, interrupted Hayward almost as soon as he began speaking, shouting, "You need to be charged with a crime!" and raising her hands, which had been darkened as if by oil.

'$20-billion shakedown'

"BP's corporate complacency is astonishing," said Waxman.

Republican Representative Joe Barton of Texas questions BP CEO Tony Hayward on Capitol Hill in Washington, D.C., on Thursday. ((Alex Brandon/Associated Press))But the leading Republican on the committee, Representative Joe Barton of Texas, took a much different tone with Hayward in his introductory remarks.

He slammed the compensation fund established by BP at the administration's request on Wednesday. The fund is intended to help individuals and businesses harmed by the spill, but Barton called the White House meeting at which administration officials urged BP to set up the fund "a $20-billion shakedown."

"I'm ashamed of what happened in the White House," Barton said.

Vice-President Joe Biden shot back at Barton during a White House press briefing less than two hours later.

"I find it incredibly insensitive, incredibly out of touch," he told reporters when pressed for comment.

In a statement, White House press secretary Robert Gibbs called it shameful that Barton would show "more concern for big corporations that caused this disaster than the fishermen, small business owners and communities whose lives have been devastated by the destruction."

Hours later, Barton said his remarks had been "misconstrued" and apologized "for that misconstruction."

Barton said he considers BP responsible for the catastrophic oil spill and that the company should "do everything possible to make good."

Spill estimates disclosed

As of Thursday morning, the BP well had gushed between 250 million and 450 million gallons of oil into the Gulf of Mexico, based on government estimates.

An image from video provided by BP on Thursday shows oil gushing from the broken wellhead in the Gulf of Mexico. ((BP/Associated Press)) Newly disclosed documents obtained by The Associated Press show that after the Deepwater Horizon sank, BP made a worst-case estimate of nine million gallons a day flowing into the Gulf of Mexico. That is far higher than the company had said publicly until this week, when the government released its own worst-case estimate of about that amount.

The undated estimate by BP appears to have been made some time last month.

In a rare piece of good news for BP these days, the drilling of a relief well meant to staunch the gushing flow of oil is ahead of schedule and could be complete in three to four weeks, U.S. Coast Guard Adm. Thad Allen said Thursday.

The rig drilling the relief well has reached nearly 3,000 metres below the sea floor and should be within three metres of the ruptured well within weeks, Allen said. It will then bore down about 300 metres to intersect with the damaged well farther underground.